Electric ground-detector.



G. A. BURNHAM.

ELEGTRIG GROUND DETECTOR. APPLICATION FILED MAR. 1, 1911.

1,055,'018,' PatentedMar.4,1913.

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UNITED STATES PATENT OFFICE.

GEORGE AUGUSTUS BURNHAM, OF GLIFTONDALE. MASSACHUSETTS, ASSIGNOR TOSEARS B. CONDIT, JR. BROOKLINE. MASSACHUSETTS.

ELECTRIC GROUND-DETECTOR.

Specification of Letters Patent.

Patented Mar. 4, 1913.

Application filed March 1. 1911. Serial No. 611.663.

To (17/ who/nit may concern:

Be it known that" I, GEORGE A. BURNHAM, a citizentiof the United States,residing at- (liftondale. in the county of Essex and State oflllassachusetts, have invented certain new and useful Improvements inElectric Ground-Detectors, of which the followiug is a full, clear, andexact specification.

This invention relates to means for indicating or recording a ground onan electric circuit, the object being to provide a ground detector whichwill be a common instrument for a plurality of lines and which willautomatically test any one of said lines several times a minute and willadmit of discriminating or selecting the grounded wire bythe use of aseries of selector switches. Devices of this kind are ordinarilyelectrostatic in character when used-in connection with high potentialcircuits.

Experience has shown that ground detectors based on electrostaticprinciples give erroneous readings on account of the fact that they areinfluenced not only by the dynamicground. but also. and principally. bystatic influences which in reality may not be coir sidered asdetrimental to the operation of the system.

.Electromagnetic devices are employed on low potential circuits whichrequire a separate instrument for each line or a common instrument maybe employed which the at tendant may transfer from one circuit to theother.,

It has been found in practice that the testing of the grounds on adistribution system when left to the discretion of the operator has.resulted in serious accidents to life and property on account of thefact that a ground might occur immediately aft-er the attendant hadtested the line, and, as a general rule, a ground being tested severaltimes a day the trouble would notbe indicated until the operator hadmade the next test on the system. This may have been a period of severalhours and in each case the Wire may have dropped into the street or aserious ground occurred which has provcn so disastrousin many cases,especially on high potential systems. Under my invention, howcvenasingle indicating or recording instrument is used which is in continuousservice, but during such service in an intermittent manner continuouslytests each of the lines connected with the device such that if a groundoccurs on the aforesaid wires an indication which may be eitheryisual 0raudible is obtained.

In circuit with the common ground wire is a. transformer which isautomatically connected or disconnected to the several lines, thesecondary of the transformer being connected to either an indicating orrecording instrument. In series with the transformer are placed severalelimination switches, affording means by which the grounded wire may beeasily selected. I maintain a contact brush in continuous movement bymeans of an electric motor or other suitable driving mechanisni andplace in its path a series of fixed contacts corresponding to theseveral wires to be tested. From a ring Contact Secured to the brush Ilead aground wirein which I insert the primary of a potentialtransformer, in the secondary of which may be placed a lamp orindicating or recording instrument of any desired character. Thus asingle instrument may serve any number of line wires with the minimumconsumption of energ since an instantaneous contact merely is requiredwhile the brush passes over the several contacts and the cir cuit isconnected with ground over a high resistance pa th through the potentialtransformer.

My invention therefore consists of a ground. detector adapted tointermittently place an indicating or recording device in circuit with agroup of electric distribution lines through a ground branch includingprotective resistance. combined with a means for switching each of thelines in'and out of the circuit at will A'fu'rther distinctive featureof my invention is that instead of'producing a slight change in theintensity placement of the needle on the indicating instrument I producea series of fiashesflashes of light or pulsating swings of theindicating needle, which is much more effective in attracting theattention of the op- Furthermore, testing of the lines does not becomepart of the operators work and is' going on continuously as long as thesystem as in operation.

In the accompanying drawing which illustrates my invention 1, 2 and 3represent bus-bars connected with the lines of the distributionpcirciiitn I have indicated three .erat-or than theaforementioned method.

such lines but any desired number may be used. From each bus-bar is abranch circuit .from a local source of supply by a worm gear 13 ismounted on the panel, the brush axis of re olution being in the centerof a circle bounding the'contacts. 1 brush 14 bears on a metallic hubconnected with a brush ll and connects with a ground through the primaryof a potential trans former 15, the secondary of which includes anindicating or recording instrument 16 of any desired kind. This may be alamp or a voltmeter or a device such, as an electric hell. I have shownin the diagram'a voltmeter.

\Vith a ground detector as thus described,-

it a ground occurs on any line of the system, the attendant will at oncenote a series of pulsations ot the indicating needle or flashes of thelamp it a lamp is used for the indicating device. Thus it will be notedthat the distribution circuits are not in normal con dition and by theuse of the elimination switches it, 5, 6, the grounded wire may belocated.

of the system there will be no indication whatever in the indicatingdevice.

Having thus described my invention, what I claim as new anddesire tosecure by Letters Patent is 2- l; The combination with the supply mains\Vhen the line is in normal condi tion and no grounds are present on anypart- I for a distribution circuit, oi a ground detector, said grounddetector comprising a lead from each of said mains, stationary contacts,one for each of said leads and connected therewith, a movable brush armsuccessively engaging said contacts, a path to ground connected to saidbrush arm. an in dicating device responsire to How and cessation of flowof current in said path, and a switch for each of said leads adapted toopen and close the same independently of the closing and opening of theswitches in the other leads, the continuity of said distribution circuitbeing independent of said switches.

' 2. The combination withthe supply mains for a distribution circuit, ofa ground detector. said ground detector comprising a contacts, one foreach of said leads and con cessively engaging said contacts, a motor fordriving said brush, a potential transformer having its high resistancewinding connect ed between said brush and ground, an indi catinginstrument in the secondary circuit of the transformer, said instrumentbeing responsive to flow and cessation of flow of currentin saidtransformer, and a switch for each of said leads adapted to open andclose the same independently of the closing and opening of the switchesin the other leads, the continuity of said distribution circuit beingindependent of said switches.

In testimony whereof I aihx my signature, in presence of two witnesses.

GEORGE AUGUSTUS BURNHAM. \Vitnesses AUSTIN F. GREENE, C. C. BADEAU.

lead from each of said mains, stationary.

nected therewith, a movable brush arm suc'

